One-component or two-component toner used in a dry development system is constituted of a binding resin, a coloring agent, a charge controlling agent and so on. Since the binding resin is a main component of the toner in the above case, characteristics such as grindability, the capacity to disperse a coloring agent and so on are required of the binder. Further, it becomes necessary for the binding resin to have many other properties including fixability, anti-offset and anti-blocking properties, electric properties and so on when the binding resin is mixed with other constituents inside the toner.
In particular, the fixation has been in need of speeding-up with an increase in developing speed. Such being the case, certain binding resins capable of ensuring easy release of toner from rolls and various types of internal mold-releasing agents have been proposed. For instance, Japanese Tokkai Hei 5-197202 (the term "Tokkai" as used herein means an "unexamined published application") proposes the block copolymer of dimethylpolysiloxane and an aromatic polyester. This block copolymer can produce a marked improvement in anti-blocking property in fact, but it requires a high temperature and a long time for the polyesterification reaction. Thus, it is undesirable from an industrial point of view. Accordingly, it has been tried to use catalysts for the acceleration of polyester condensation, such as organotin compounds, in order to proceed the polyesterification reaction at a low temperature. However, it cannot be said that those tin compounds are not detrimental to health.
As the internal mold-releasing agent, on the other hand, there have been proposed liquids of the kind which have low surface energy, such as dimethylsilicone oil (U.S. Pat. No. 4,517,272). However, it has been pointed out that the silicone oil soiled the carrier particles. After the soiling with silicone oil, the developer comes to be short of triboelectricity, and so it becomes difficult to consistently charge the toner.
As a result of our intensive studies for solving the above-described problems, it has been found out that dimethylsiloxane-grafted acrylate copolymers are suitable for a binder of toner in view of not only their physical properties but also easiness of production, thereby achieving the present invention.